In the area of digital cameras, a known technique in the related art provides computational photography for extracting image data on a subject and further information from the output of an image sensor and applying the information to image processing. An example is the process of acquiring information on a distance to a subject from image data acquired by a digital camera.
A known method for acquiring distance information from image data is a stereo matching method based on the correlation among a plurality of image data having parallax (PTL 1). Another known method is a method for acquiring distance information on the basis of the difference in in-focus state among a plurality of images in different in-focus states (PTL 2).
Since the above distance-information acquisition processes require complicated calculation, a method of executing the processes using, not a camera, but an external device, during acquisition of image data is conceivable.
However, this method is not convenient because the process for acquiring distance information differs depending on the kind of input image data, which needs dedicated processing software and hardware for the individual image data.